The present invention relates generally to the processing of coal tar, and in particular to the treatment of a high-solids coke oven coal tar to remove ash and other solids and recover a modified coal tar suitable for distillation to produce binder pitch.
As further background, coal tars are generated as by-products of coking processes in the steel industry. Coal tars are complex chemical mixtures containing aromatic chemicals and various solids, and their particular composition varies widely depending largely upon the coking process by which they are produced. Some modern coking processes lead to coal tars having very high solids contents. These tars are problematic because they are unsuitable for customary uses for coal tars and thus can generate high disposal costs.
Two important solid components of coal tars are ash and quinoline insoluble ("QI") components. Ash is generally known in the coal tar industry as the noncarbonaceous inorganic contaminant component of coal tar with a typical particle size greater than about 25 micrometers, with the major ash component being silicon. On the other hand, QI components are fine carbonaceous particles, generally 1 micrometer or less in particle size.
One use for coal tar is for the production of binder pitch which in turn is used in large volumes in the aluminum industry in the preparation of anodes. The binder pitch is prepared by distillation of the coal tar. To be suitable for distillation to binder pitch, a coal tar must have defined levels of ash and QI components. However, as noted above, some modern coking operations produce high-solids coal tars which have high levels of ash and QI components--levels that are far too high to be useful to prepare binder pitch. As such, there is a need for a process for treating ash-containing high-solids coal tars to produce modified coal tars that are suitable for the production of binder pitch. Such a process should be practicable on a large scale and maximize recovery of valuable products from the treated tars. The present invention addresses these needs.